It wouldn't be an upgrade over Maroney, but a possible upgrade over Morris. Keep in mind that we still don't even know Sammy's health status for 2008 coming off what can be a serious injury, and he'll turn 31 this month. Also, I thought Morris did well in 2007, but he wasn't better than Maroney, and only really had two/three good games, which came against sub par run defenses.
I'd honestly rather draft Jonathan Stewart in the second round (he might fall after word of his toe injury), but I wouldn't be surprised if the Patriots looked at Alexander, if he came at a reasonable/cheap price. Once the Seahawks signed Julius Jones I actually wondered if a released Alexander would be of interest to BB...
Also, Morris can play FB, so they could release Eckel and have Morris compete with Evans at FB and either Stewart (who I'd prefer) or Alexander at RB. This would increase depth and upgrade both positions.